In general, textiles (material or fabric) are used in our daily lives as clothes, bedclothes, and the like.
When an electronic technology is applied to the textile, smart textile products having new functions, such as heating clothes, electronic protective gears, heath monitoring, rehabilitation treatment and the like can be realized.
A smart textile is a representative technology for realizing the era of ubiquitous and refers to a new type of future textile in which an information technology (IT), a nanotechnology (NT), a biotechnology (BT), an environmental technology (ET), and the like are interconnected.
As a result of various kinds of research conducted for realizing a smart textile, in order to carry electric current and provide shielding from an electric field, technologies of including a conductive yarn in a yarn and including metal coated yarns have been publicly known. These electrically conductive metal composite yarns have been fabricated as fabrics and clothing products.
As such, the electrically conductive metal composite yarns are used in the smart textile combined with an electronic technology, thereby enabling electronic functions such as the supply of electricity, the transmission of signals, touch sensing, or the like to be performed.
Conventional arts relating to the electrically conductive metal composite yarns which can be used in the smart textile are Korean Patent No. 0688899 entitled “Electric conduction strong metal complex thread manufacturing method and electric conduction strong metal complex thread using the method,” Korean Patent No. 0895092 entitled “Electrically conductive sewing thread for power and data transmission line of smart interactive textile systems,” Korean Patent No. 1015563 entitled “Electrically conductive metal composite embroidery yarn and embroidered circuit using thereof,” and the like.
In the conventional arts, the electrically conductive metal composite yarn is produced by a first process of wrapping multiple strands of a conductive yarn around the surface of a yarn in a covered state to form a large number of twists per meter, a second process of performing ply twist to the right to form a large number of twists per meter in a state of wrapping the conductive yarn around the surface of the yarn through the first process, a third process of performing ply twist to the left to form a large number of twists per meter by plaiting the conductive yarn which is ply-twisted to the right by the second process.
The electrically conductive metal composite yarn produced by the manufacturing method according to the conventional art is problematic in that yield strength of the conductive yarn is weak.
In other words, checking an embroidered circuit of a smart textile made by an embroidery process, the regularity of electric resistance of the embroidered circuit is non-uniform.
This is because when the electrically conductive metal composite yarn stretches due to an external force applied during an embroidery process as the yield strength of the conductive yarn in the electrically conductive metal composite yarn is weak, the conductive yarn in the inside thereof stretches or is cut.
In order to overcome this problem, the electrically conductive metal composite yarn should be prevented from stretching due to an external force applied to the composite yarn during the embroidery process.
In general, the strength of thread is increased according to an increase of the number of twists per meter, but in order for strength of the electrically conductive metal composite yarn to increase by increasing the number of twists per meter thereof, because a torque occurs, feeding the electrically conductive metal composite yarn is interrupted during the embroidery process, and an increase in the number of twists per meter beyond the range of a limit also causes a problem of continuous elongation of the metal filament (the conductive yarn) in the structure of the electrically conductive metal composite yarn. Thus, in order to minimize a variation in electric resistance of the conductive yarn by preventing the electrically conductive metal composite yarn from stretching due to the external force during the embroidery process, a method increasing yield strength of the conductive yarn rather than a method of increasing strength by simply increasing the number of twists per meter should be used.
However, since the electrically conductive metal composite yarn produced by the conventional arts has weak yield strength in terms of the conductive yarn in the inside thereof, checking an embroidered circuit produced using the same, the regularity of electric resistance is non-uniform.
Furthermore, among the conventional arts, Korean Patent No. 1015563 entitled “Electrically conductive metal composite embroidery yarn and embroidered circuit using thereof,” which is directed to covering a metal filament yarn (i.e. conductive yarn) using a protective thread (i.e. yarn) of 30 denier or less, has the following several problems.
First, it is very difficult to practically produce a metal composite yarn having a uniform and thin thickness and uniform appearance using a method of covering a general yarn with a metal covered yarn formed by wrapping a metal filament yarn (i.e. conductive yarn) around a general yarn having a thin thickness of 30 denier or less.
Second, even if such a metal composite yarn is made, with regard to the electrically conductive metal composite yarn produced by using the conductive yarn covered with the general yarn for protection, it is difficult to cause electrical contact among the conductive yarns in the inside of threads, and accordingly, when a defect is generated at a specific part of the conductive yarn inside the electrically conductive metal composite yarn, a variation in electric resistance of the embroidered circuit will be largely increased.
Third, electrical contact among the embroidered circuits produced using the electrically conductive metal composite yarn as well as the electrical contact among conductive yarns inside the electrically conductive metal composite yarn may not be utilized in producing a necessary sensing structure.